The present invention relates to anodic bonding and, more particularly, to an anodic bonding method which can favorably bond a substrate material and a glass member through a metal film.
Conventionally, there has been known a so-called anodic bonding method in which a boric acid glass and silicon are stacked and heated up to a temperature lower than a glass melting point to bond between the both by applying a direct current voltage of several hundreds of volts with a silicon side rendered as an anode. This method is often used in the field of semiconductor devices.
However, this anodic bonding method is usually conducted by heating up to approximately 300-400xc2x0 C. There is a problem in that, where the materials to be bonded are largely different in thermal expansion coefficient, it is difficult to achieve a favorable bonding. That is, where there is a difference in thermal expansion coefficient, crack or breakage tend to occur as the temperature increases. For example, in the case of a bonding temperature of approximately 300-400xc2x0 C. as mentioned above, it is considered that the difference in thermal expansion coefficient of members to be bonded is limited to 2 ppm/xc2x0 C. at most. Due to this, this anodic bonding method has been in use limited to the case of bonding between materials close in thermal expansion coefficient. Accordingly, despite the fact that there have been reports concerning anodic bonding methods between metals and glass, no actual products have been found.
The present invention has been made in view of such circumstances, and it is an object to provide an anodic bonding method which can bond well between members different in thermal expansion coefficient.
A first aspect of the invention for solving the above problem is an anodic bonding method for applying a voltage to and bonding between a first member having a bonding film on a bonding surface and a second member closely put on the bonding surface of the first member through the bonding film in a manner such that the first member is rendered as an anode, wherein the bonding film is formed of a metal film and the second member is formed of a soda-lime glass, and a bonding temperature is at 100-200xc2x0 C. and an application voltage is at 0.5-5.0 kV.
A second aspect of the invention is an anodic bonding method wherein, in the first aspect, the metal film is selected from the group consisting of aluminum, chromium and an alloy of these metals.
In accordance with the invention as described above, due to conducting anodic bonding at low temperature it is possible to bond well between members different in thermal expansion coefficient through a metal film.